Re: what did you do to your motorized bicycle today?
It could be from the rain if the bike has to be stored outside... I had that problem with my 84 Kawasaki KZ700 and it would bearly run after a hard rain but I found out it could take in water from the vent on the gas cap so I started taping a plastic bag to the tank to cover the cap if it was going to rain hard when I rode it to work and problem solved.
The condensation tho can't be totally ruled out if the bike is parked outside or just from the high humidity from all the rain etc since the alcohol in the fuel can absorb lots of water as well.
Easiest thing to do if you have to store the bike outdoors would be to just cover the tank with a plastic bag so rain water can't find it's way past the cap, it won't help for condensation but it will stop rain from getting in.